This invention relates to a method of installing and removing a locking device for a two-part earth working tool and, more particularly to a method utilizing a unitary device which provides a secure lock during the usual operation of the tool but which is readily removable for replacement of the wearable part of the tool.
The usual dilemma facing workers in the excavating field is to provide an outer or earth engaging element which is reliably secured to the support or holder during normal operation -- but which is conveniently and readily detachable for replacement. Examples of such elements are the point parts of excavating teeth, shrouds for rippers and buckets, bit for scrapers, etc.
It will be appreciated that the element or wearable portion of the tool engaging the ground wears in an accelerated rate relative to the remainder of the tool. Very often a holder may have a life at least equal to the wear lives to 5 to 10 earth engaging elements provided thereon. Should the wearable element become inadvertently detached during normal operation -- and here it is to be appreciated that normal operation contemplates severe shock and impact loads from time to time -- the valuable holder may be seriously damaged. The equipment utilizing these tools is quite expensive and, in many cases, is used in remote areas so major repair is a serious problem. Thus, the principal requirement of a locking device for holding the wearable part on the support portion part of the tool is that the locking device is secure and reliable during this normal operation.
At the same time, however, because the expensive nature of the equipment, it is equally necessary to have the wear part replacement achieved with a minimum of time and labor. Many different kinds of methods utilizing locking devices have been provided over the years for this purpose. Perhaps the most intensively worked area has to do with excavating teeth (U.S. Classification 37-141, 142). Since about the turn of the century, workers in the excavating art have preferred two-part teeth where the point or tip is removable after it has become dull. By providing the tooth or tool in two parts, the amount of "throwaway" metal in the worn part is minimized. This economic consideration made it necessary to develop keys or locking devices for the two parts. Some of the early workers made use of deformable keys such can be seen in U.S. Pat. No. 2,055,265. For the most part, this type of lock has been long since discarded. If the deformed key or pin is strong enough to bear up under the harsh impacts, it became difficult to remove, particularly since it would become compacted with earth, rock dust, etc. Introducing a chisel or other deforming instrument was time consuming and often ineffective.
The same defects attended the nut and bolt type of lock (exemplified by U.S. Pat. No. 2,385,395). Removal was difficult because a powerful withdrawing force was difficult to apply. The threads could literally become closed with compacted material.
Therefore, the art turned pretty uniformly to a two-part locking device, one popular form being seen in U.S. Pat. No. 2,483,032. Generally, such devices included a metal pin of substantially rigid construction in combination with a resilient or deformable plug, usually rubber. The pin or key when driven into the aligned openings of the two-part tool would deform the rubber plug and achieve a seat, drawing the two parts of the tool tightly together. Such locking devices (which are still widely used) have the advantage of low cost because of simplicity of manufacture but have the drawback of requiring two pieces for the lock with the attendant possibility of loss and incompatibility of the two parts when the same are mass produced.
The last genre of locking device is a unitary pin of "sandwich" constuction, as exemplified by U.S. Pat. No. 3,020,655. In this class of device, the resilient material is incorporated as an integral part of the pin so that only a single element is required. This avoids the drawback of having two pieces to the lock but usually is more expensive to produce. Even more importantly, as far as the art is concerned, there had been doubts as to the ability of the sandwich type lock to provide the secure attachment required. Because of its very nature in being a unitary piece, the range of design variations available was restricted -- as compared with the more popular two-piece locks.
One attempt to improve the unitary type of locking device is seen in U.S. Pat. No. 3,511,126. There, a portion of the sandwich was provided eccentric to the normally cylindrical contour to improve the holding power of the lock. However, this lock structure resisted removal by the normal and desired method of applying a dislodging force along the axis of the pin lock. Therefore, the desired ease of removal, a principal characteristic of a superior method of utilizing a locking device, was not present. Also, because the intermediate portion of the locking device was eccentrically enthickened, there was a substantial chance of shearing the intermediate portion and destroying the locking device.
When such shearing occurred, expensive down time resulted because artisans in the field normally expected the locking device to last the life of the holder and when replacing wearable elements such as points, shrouds, bits, etc., carry only the minimum replacement parts into the field. Here, it should be appreciated that the wearable parts are quite heavy notwithstanding the desirability of reducing the amount of throw away metal, being made of cast alloy steel, and therefore anything that guarantees easy of the method of replacement -- such as not having to be concerned about replacing destroyed locking devices -- is of substantial importance and advantage. As a consequence, the lock construction of U.S. Pat. No. 3,511,126 did not find favor with the workers in the excavating art.
The instant invention constitutes an improvement in the sandwich type of locking device and achieves the foregoing goals of secure mounting and ready dismantling without the disadvantages of the prior art -- realizing this through the provision of a method utilizing a locking pin which has a pair of intermediate portions enthickened relative to the cylindrical contour of the pin in diametrically opposed positions and which include bearing pieces resiliently secured to the main body of the pin whereby the steps of installation and removal include the application of balanced forces on the bearing pieces to avoid shearing thereof.
Other advantages and characteristics may be seen in the details of construction and operation set down in the ensuing specification.